The term Pteridospermatophyta (or "seed ferns" or "Pteridospermatopsida") refers to several distinct polyphyletic groups of extinct seed-bearing plants (spermatophytes). The earliest fossil evidence for plants of this type is the genus Elkinsia of the late Devonian age. They flourished particularly during the Carboniferous and Permian periods. Pteridosperms declined during the Mesozoic Era and had mostly disappeared by the end of the Cretaceous Period, though some pteridosperm-like plants seem to have survived into Eocene times, based on fossil finds in Tasmania.
The concept of pteridosperms goes back to the late 19th century when palaeobotanists came to realise that many Carboniferous fossils resembling fern fronds had anatomical features more reminiscent of the modern-day seed plants, the cycads. In 1899 the German palaeobotanist Henry Potonié coined the term "Cycadofilices" ("cycad-ferns") for such fossils, suggesting that they were a group of non-seed plants intermediate between the ferns and cycads. Shortly afterwards, the British palaeobotanists Frank Oliver and Dukinfield Henry Scott (with the assistance of Oliver's student at the time, Marie Stopes) made the critical discovery that some of these fronds (genus Lyginopteris) were associated with seeds (genus Lagenostoma) that had identical and very distinctive glandular hairs, and concluded that both fronds and seeds belonged to the same plant. Soon, additional evidence came to light suggesting that seeds were also attached to the Carboniferous fern-like fronds Dicksonites, Neuropteris and Aneimites. Initially it was still thought that they were "transitional fossils" intermediate between the ferns and cycads, and especially in the English-speaking world they were referred to as "seed ferns" or "pteridosperms". Today, despite being regarded by most palaeobotanists as only distantly related to ferns, these spurious names have nonetheless established themselves. Nowadays, four orders of Palaeozoic seed plants tend to be referred to as pteridosperms: Lyginopteridales, Medullosales, Callistophytales and Peltaspermales.
Their discovery attracted considerable attention at the time, as the pteridosperms were the first extinct group of vascular plants to be identified solely from the fossil record. In the 19th century the Carboniferous Period was often referred to as the "Age of Ferns" but these discoveries during the first decade of the 20th century made it clear that the "Age of Pteridosperms" was perhaps a better description.
During the 20th century the concept of pteridosperms was expanded to include various Mesozoic groups of seed plants with fern-like fronds, such as the Corystospermaceae. Some palaeobotanists also included seed plant groups with entire leaves such as the Glossopteridales and Gigantopteridales, which was stretching the concept. In the context of modern phylogenetic models, the groups often referred to as pteridosperms appear to be liberally spread across a range of clades, and many palaeobotanists today would regard pteridosperms as little more than a paraphyletic 'grade-group' with no common lineage. One of the few characters that may unify the group is that the ovules were borne in a cupule, a group of enclosing branches, but this has not been confirmed for all "pteridosperm" groups.
With regard to the enduring value of the division, many palaeobotanists still use the pteridosperm grouping in an informal sense to refer to the seed plants that are not angiosperms, coniferoids (conifers or cordaites), ginkgophytes or cycadophytes (cycads or bennettites). This is particularly useful for extinct seed plant groups whose systematic relationships remain speculative, as they can be classified as pteridosperms with no valid implications being made as to their systematic affinities. Also, from a purely curatorial perspective the term pteridosperms is a useful shorthand for describing the fern-like fronds that were probably produced by seed plants, which are commonly found in many Palaeozoic and Mesozoic fossil floras.
|Fossil seed fern leaves from the Late Carboniferous of northeastern Ohio.|
An alternative phylogeny of spermatophytes based on the work by Novíkov & Barabaš-Krasni 2015 with plant taxon authors from Anderson, Anderson & Cleal 2007 showing the relationship of extinct clades.
The Alethopteridaceae are a family of extinct plants belonging to Pteridospermatophyta, or seed ferns.Alethopteris
Alethopteris is a prehistoric plant genus of fossil Pteridospermatophyta (seed ferns) that developed in the Carboniferous period (around 360 to 300 million years ago).It is in the family Alethopteridaceae.Callipteridium
Callipteridium is an extinct genus of pteridospermous seed ferns belonging to the family Cyclopteridaceae. These ferns existed in the Carboniferous period.Caytonia
Caytonia is an extinct genus of seed ferns.Caytoniaceae
The Caytoniaceae are an extinct family of plants belonging to Pteridospermatophyta, or seed ferns.Corystospermaceae
Corystospermaceae is a natural family of seed ferns (Pteridospermatophyta) also called Umkomasiaceae, and first based on fossils collected by Hamshaw Thomas from the Burnera Waterfall locality near the Umkomaas River of South Africa
The leaves of Dicroidium were recognized by Alex Du Toit
to unite all the countries of the Gondwana supercontinent during the Triassic: Africa, South America, India, and Australia. Subsequently, Dicroidium was found in the Triassic of Antarctica and New Zealand, and also the Permian of
Jordan. According to the form generic system of paleobotany, leaves are given separate generic names to ovulate and pollen organs, but the discovery of these reproductive organs in Africa by Thomas, and subsequently throughout Gondwana, strengthened Du Toit's concept of a continuous southern supercontinent.Cyclopteris
Cyclopteris is an extinct genus of seed ferns in the extinct family †Cyclopteridaceae. Species are from the Carboniferous.
Cyclopteris elegans Lesquereux, 1854 - from the Carboniferous of Pennsylvania, USA
Cyclopteris elegans Unger, 1858
Cyclopteris elegans Achepohl, 1883 - from Westphalia, GermanyDicroidium
Dicroidium is an extinct genus of fork-leaved seed ferns that were distributed over Gondwana during the Triassic (252 to 201 million years ago). Their fossils are known from South Africa, Australia, New Zealand, South America and Antarctica. They were first discovered in Triassic sediments of Tasmania by Morris in 1845. Fossils from the Umm Irna Formation in Jordan indicate that these plants already existed in Late Permian.Glossopteridales
Glossopteridales is an extinct order of plants belonging to Pteridospermatophyta, or seed ferns, also known as Arberiales and Ottokariales. They arose at the beginning of the Permian (298.9 million years ago) on the southern continent of Gondwana, but became extinct before the end of the Permian period (251.902 million years ago). The best known genus is Glossopteris. Other examples are Glossotheca and Vertebraria.
Permian permineralised glossopterid reproduction organs found in the central Transantarctic Mountains suggest seeds had an adaxial attachment to the leaf-like mega-sporophyll. This indicate Glossopteridales can be classified as seed ferns and is important in determining the status of the group as either close relatives or ancestors of the angiosperms.Midrib-less forms were common in the Early Permian whereas midrib forms were more common in the Late Permian.Glossopteris
Glossopteris (Ancient Greek: γλώσσα glossa, meaning "tongue", because the leaves were tongue-shaped, and pteris, Greek for fern or feathery) is the largest and best-known genus of the extinct order of seed ferns known as Glossopteridales (also known as Arberiales or Ottokariales). The genus Glossopteris refers only to leaves, within a framework of form genera used in paleobotany. (For likely reproductive organs see Glossopteridaceae.) These are important because they indicate biological identity of these plants that were critical for recognizing former connections between the various fragments of Gondwana: South America, Africa, India, Australia, New Zealand, and Antarctica.Lepidopteris
Lepidopteris ("pleasant fern") is a form genus for leaves of Late Permian to Late Triassic Period Pteridospermatophyta, or seed ferns, which lived from around 260 to 200 million years ago in what is now Australia, Antarctica, India, South America, South Africa, Russia and China. Nine species are currently recognized.Lepidopteris was a common and widespread seed fern, which survived the Permian-Triassic extinction event but succumbed to the Triassic-Jurassic extinction event. Lepidopteris callipteroides is especially common between the first two episodes of Permian-Triassic extinction event, and L. ottonis forms a comparable acme zone immediate before the Triassic-Jurassic extinction event.Lyginopteris
Lyginopteris is a genus of Late Carboniferous seed fern stems with a very distinctive outer cortex of sclereids forming a pattern in cross section like Roman numerals on a clock face, often called a Sparganum cortex. Some Lyginopteris were parasitized by water molds.Neuropteris
Neuropteris is an extinct seed fern that existed in the Carboniferous period, known only from fossils.
Major species include Neuropteris loschi.Pachypteris
Pachypteris (Brongn.) T.M.Harris. is a Mesozoic pteridosperm leaf fossil probably belonging to the seed fern Order Peltaspermales.Peltaspermaceae
Peltaspermaceae is a natural family of seed ferns (Pteridospermatophyta) widespread in both northern and southern hemispheres coal measures of Permian and Triassic age.Peltaspermales
The Peltaspermales are an extinct order of plants belonging to Pteridospermatophyta, or seed ferns. It is unclear whether they form a natural group of organisms as they are poorly known. It has been suggested that they survived the Cretaceous–Paleogene extinction event.Pteruchus
Pteruchus is a form genus for pollen organs of the seed fern (Pteridospermatophyta family Umkomasiaceae. It was first described by Hamshaw Thomas from the Umkomaas locality of South Africa.Sagenopteris
Sagenopteris is a genus of extinct seed ferns from the Triassic to late Early Cretaceous.Sphenopteris
Sphenopteris is a genus of seed ferns containing the foliage of various extinct plants, ranging from the Devonian to Late Cretaceous.